More than half the earth's land area was once
forest. Now, the figure is less than one-third - around 3
400 million hectares. Forests are cleared and degraded at
a rate of 300 000 hectares per week.

The world's forests
cover some 3 400 million hectares - an area the size of North and
South America combined. They are sources of raw materials and
food, and are essential for maintaining agricultural productivity
and the environmental well-being of the planet as a whole.

Trees and forests anchor the soil and buffer the winds, thus
protecting against erosion by wind and water. They produce oxygen
and absorb carbon dioxide, the major agent in global warming.
They intercept rainfall, releasing it slowly into soils, surface
waters and underground aquifers. The water vapour released from
their foliage in transpiration influences climate and is a vital
part of the hydrological cycle.

Forests and woodlands vary from the dense rainforests of the
tropics to East Africa's open woodland savannahs; from mangroves
to the mixed temperate broadleaved and boreal forests. But
unmanaged harvesting, ill-planned clearance for farming, or
physiological pressures from pollution can pose a threat to any
forest type.

During the 1980s more than 15 million hectares of tropical
forests were lost each year: the overwhelming majority of the
deforestation was intended to provide land for agriculture. The
largest losses occurred in tropical moist deciduous forests, the
areas best suited for settlement and farming. The extent of these
forests declined by 61 million hectares - more than 10 percent of
their area -while 46 million hectares, or 60 percent, of tropical
rainforests were lost. Few of these areas have been replanted.

Tree cover is increasing in many temperate regions, mainly due
to the establishment of forest plantations. Europe increased its
forest and wooded land by 2 percent over the 1980s and there were
small increases in New Zealand and Australia. In the same decade,
however, a drop of some 3.5 million hectares occurred in the
United States. The area of the former USSR reported an increase
between 1978 and 1988. However, there is an urgent need to bring
many of the Siberian forests under sustainable management to
avoid their degradation. As well as managing some forests for
production, diversity should be preserved in others by
designating protected areas.

Many forests in industrialized countries have been damaged by
airborne pollutants, including acid rain: the International
Institute for Applied Systems Analysis (IIASA) has estimated that
US$ 60 000 million would have to be spent annually for 25 years
to protect Europe's forests from pollution.